Tuning Carbon Dioxide Adsorption Affinity of Zinc(II) MOFs by Mixing Bis(pyrazolate) Ligands with N-Containing Tags

The four zinc(II) mixed-ligand metal-organic frameworks (MIXMOFs) Zn(BPZ)x(BPZNO2)1-x, Zn(BPZ)x(BPZNH2)1-x, Zn(BPZNO2)x(BPZNH2)1-x, and Zn(BPZ)x(BPZNO2)y(BPZNH2)1-x-y (H2BPZ = 4,4′-bipyrazole; H2BPZNO2 = 3-nitro-4,4′-bipyrazole; H2BPZNH2 = 3-amino-4,4′-bipyrazole) were prepared through solvothermal routes and fully investigated in the solid state. Isoreticular to the end members Zn(BPZ) and Zn(BPZX) (X = NO2, NH2), they are the first examples ever reported of (pyr)azolate MIXMOFs. Their crystal structure is characterized by a three-dimensional open framework with one-dimensional square or rhombic channels decorated by the functional groups. Accurate information about ligand stoichiometric ratio was determined (for the first time on MIXMOFs) through integration of selected ligands skeleton resonances from 13C cross polarized magic angle spinning solid-state NMR spectra collected on the as-synthesized materials. Like other poly(pyrazolate) MOFs, the four MIXMOFs are thermally stable, with decomposition temperatures between 708 and 726 K. As disclosed by N2 adsorption at 77 K, they are micro-mesoporous materials with Brunauer-Emmett-Teller specific surface areas in the range 400-600 m2/g. A comparative study (involving also the single-ligand analogues) of CO2 adsorption capacity, CO2 isosteric heat of adsorption (Qst), and CO2/N2 selectivity in equimolar mixtures at p = 1 bar and T = 298 K cast light on interesting trends, depending on ligand tag nature or ligand stoichiometric ratio. In particular, the amino-decorated compounds show higher Qst values and CO2/N2 selectivity vs the nitro-functionalized analogues; in addition, tag "dilution" [upon passing from Zn(BPZX) to Zn(BPZ)x(BPZX)1-x] increases CO2 adsorption selectivity over N2. The simultaneous presence of amino and nitro groups is not beneficial for CO2 uptake. Among the compounds studied, the best compromise among uptake capacity, Qst, and CO2/N2 selectivity is represented by Zn(BPZ)x(BPZNH2)1-x

Cobalt(II) Bipyrazolate Metal-Organic Frameworks as Heterogeneous Catalysts in Cumene Aerobic Oxidation: A Tag-Dependent Selectivity

"This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c00481"[EN] Three metal-organic frameworks with the general formula Co(BPZX) (BPZX(2-) = 3-X-4,4'-bipyrazolate, X = H, NH2, NO2) constructed with ligands having different functional groups on the same skeleton have been employed as heterogeneous catalysts for aerobic liquid-phase oxidation of cumene with O-2 as oxidant. O-2 adsorption isotherms collected at p(O2) = 1 atm and T = 195 and 273 K have cast light on the relative affinity of these catalysts for dioxygen. The highest gas uptake at 195 K is found for Co(BPZ) (3.2 mmol/g (10.1 wt % O-2)), in line with its highest BET specific surface area (926 m(2)/g) in comparison with those of Co(BPZNH(2)) (317 m(2)/g) and Co(BPZNO(2)) (645 m(2)/g). The O-2 isosteric heat of adsorption (Q(2)) trend follows the order Co(BPZ) > Co(BPZNH(2)) > Co(BPZNO(2)). Interestingly, the selectivity in the cumene oxidation products was found to be dependent on the tag present in the catalyst linker: while cumene hydroperoxide (CHP) is the main product obtained with Co(BPZ) (84% selectivity to CHP after 7 h, p(O2) = 4 bar, and T = 363 K), further oxidation to 2-phenyl-2-propanol (PP) is observed in the presence of Co(BPZNH(2)) as the catalyst (69% selectivity to PP under the same experimental conditions).S.G., R.V., and M.M. acknowledge Universita dell'Insubria for partial funding. G.G. thanks the Italian MIUR through the PRIN 2017 Project Multi-e: Multielectron Transfer for the Conversion of Small Molecules: an Enabling Technology for the Chemical Use of Renewable Energy (20179337R7) for financial support. G.G. thanks the TRAINER project (Catalysts for Transition to Renewable Energy Future) ref. ANR-17-MPGA-0017 for support. C.P. thanks the University of Camerino and the Italian MIUR throughout the PRIN 2015 Project Towards a Sustainable Chemistry (20154 x 9ATP_002). This project has also received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 641887 (project acronym: DEFNET) and the Spanish Government through projects MAT2017-82288-C2-1-P and Severo Ochoa (SEV-2016-0683). Professor Norberto Masciocchi (University of Insubria, Como, Italy) is acknowledged for fruitful discussions. The authors are also grateful to Dr. Giulia Tuci (CNR-ICCOM Florence, Italy) for help with the XPS curve fitting. The Microscopy Service of the Universitat Politècnica de València is gratefully acknowledged for the electron microscopy measurements.Nowacka, AE.; Vismara, R.; Mercuri, G.; Moroni, M.; Palomino Roca, M.; Domasevitch, K.; Di Nicola, C.... (2020). Cobalt(II) Bipyrazolate Metal-Organic Frameworks as Heterogeneous Catalysts in Cumene Aerobic Oxidation: A Tag-Dependent Selectivity. Inorganic Chemistry. 59(12):8161-8172. https://doi.org/10.1021/acs.inorgchem.0c00481S816181725912Fortuin, J. P., & Waterman, H. I. (1953). Production of phenol from cumene. Chemical Engineering Science, 2(4), 182-192. doi:10.1016/0009-2509(53)80040-0Luyben, W. L. (2009). Design and Control of the Cumene Process. Industrial & Engineering Chemistry Research, 49(2), 719-734. doi:10.1021/ie9011535Matsui, S., & Fujita, T. (2001). New cumene-oxidation systems. 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Nitro-functionalized Bis(pyrazolate) Metal–Organic Frameworks as Carbon Dioxide Capture Materials under Ambient Conditions

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim The metal–organic frameworks (MOFs) M(BPZNO2) (M=Co, Cu, Zn; H2BPZNO2=3-nitro-4,4′-bipyrazole) were prepared through solvothermal routes and were fully investigated in the solid state. They showed good thermal stability both under a N2 atmosphere and in air, with decomposition temperatures peaking up to 663 K for Zn(BPZNO2). Their crystal structure is characterized by 3D networks with square (M=Co, Zn) or rhombic (M=Cu) channels decorated by polar NO2 groups. As revealed by N2 adsorption at 77 K, they are micro-mesoporous materials with BET specific surface areas ranging from 400 to 900 m2 g−1. Remarkably, under the mild conditions of 298 K and 1.2 bar, Zn(BPZNO2) adsorbs 21.8 wt % CO2 (4.95 mmol g−1). It shows a Henry CO2/N2 selectivity of 15 and an ideal adsorbed solution theory (IAST) selectivity of 12 at p=1 bar. As a CO2 adsorbent, this compound is the best-performing MOF to date among those bearing a nitro group as a unique chemical tag. High-resolution powder X-ray diffraction at 298 K and different CO2 loadings revealed, for the first time in a NO2-functionalized MOF, the insurgence of primary host–guest interactions involving the C(3)–NO2 moiety of the framework and the oxygen atoms of carbon dioxide, as confirmed by Grand Canonical Monte Carlo simulations. This interaction mode is markedly different from that observed in NH2-functionalized MOFs, for which the carbon atom of CO2 is involved

Synthesis and structural characterization of metal azolate/carboxylate frameworks incorporating the 1-H-pyrazol-3,4,5-tricarboxylate ligand

The tetratopic ligand 1-H-pyrazol-3,4,5-tricarboxylic acid (H4PZTC) has been used for the first time to prepare the new metal azolate/carboxylate (MAC) frameworks [Co3(HPZTC)2(H2O)6]·2H2O (MAC-1), [Co(H2PZTC)(DMF)(H2O)]2 (MAC-2) and [Cd2(PZTC)(H2O)2] (MAC-3), along either conventional or solvothermal routes. As assessed by thermogravimetric analysis, before decomposition the three MAC frameworks undergo partial decarboxylation over 200 °C. Powder X-ray diffraction unveiled 1-D chains alternating monomeric and dimeric units in MAC-1, 1-D hydrogen bonded strands of dimeric units in MAC-2 and a 3-D non-porous network in MAC-3

Powder X-ray diffraction investigation of a NO2-tagged MOF with high affinity to CO2 at mild conditions

oncerns about global warming has prompted research at the academic and industrial level to reduce anthropogenic CO2 emissions. A number of approaches exist for CO2 capture and storage from power plants emissions [1], among which the use of nanoporous adsorbents such as metal-organic frameworks (MOFs) [2]. MOFs’ performances in CO2 adsorption have been optimized also through the use of properly functionalized ligands. As, to the best of our knowledge, the NO2-function is still under-investigated [3], we have recently designed the ligand H2BPZ-NO2 (H2BPZ-NO2 = 3-nitro-4,4’-bispyrazole) and isolated the corresponding Co(II), Cu(II) and Zn(II) MOFs [4]. As disclosed by lab PXRD, irrespective of their metrics these MOFs show 3D (4,4)-connected networks with 1D square (Zn, Co) or rhombic (Cu) channels decorated by BPZ-NO22- ligands, and accounting for an empty volume of ~ 14-35%. As witnessed by TGA and variable-temperature PXRD, while Cu(BPZ-NO2) and Co(BPZ-NO2) are moderately stable (Tdec ~ 583 K and ~ 643 K respectively), Zn(BPZ-NO2) is remarkably robust (Tdec ~ 743 K), without phase change or framework collapse prior to decomposition. If exposed to H2O(v) for 7 days, Zn(BPZ-NO2) begins losing crystallinity, which is nonetheless restored upon suspension in DMF. After thermal activation, Zn(BPZ-NO2) adsorbs 22 wt % CO2 at the rather mild conditions of 298 K and 1 bar, hence ranking among the best performing MOFs under the same experimental conditions [3]. Moreover, at 298 K it shows the significant CO2/N2 selectivity of 25 ( power plants emissions consist of mixtures of N2:CO2 ~ 85:15 v/v ). Overall, these results provide important information to shed light on the chemical and structural properties a host should possess for efficient CO2 adsorption already at rather mild conditions

Crystal structure of cis-bis(μ-β-alanine-κ2O:O′)bis-[trichloridorhenium(III)](Re-Re) sesquihydrate

The structure of the title compound, [Re2Cl6(C3H7NO2)2]1.5H2O, comprises a dinuclear complex cation [Re - Re = 2.2494 (3) Å] involving cis-oriented double carboxylate bridges, four equatorial chloride ions and two weakly bonded chloride ligands in the axial positions at the two rhenium(III) atoms. In the crystal, two complex molecules and two water molecules constitute hydrogen-bonded dimers, while an extensive hydrogen-bonding network involving the groups of the zwitterionic ligand is important for generation of the framework. An additional partially occupied water molecule is disordered over two sets of sites about a symmetry centre with a site-occupancy ratio of 0.3:0.2

1,3-Bis(1,2,4-triazolyl)adamantine-based Coordination Polymers

The hybrid organic-inorganic materials known as coordination polymers are continuously gaining ground of scientific research, especially due to the interesting and promising functionalities they possess, e.g. magnetic, optical, electrical, redox, and luminescence properties, as well as, when permanent porosity is present, gas adsorption or separation, catalytic activity, and drug delivery. The reaction of the flexible ligand 1,3-bis(1,2,4-triazolyl)adamante (tr2ad, Scheme 1) with chlorides of different late transition metals, either following conventional routes or under solvothermal conditions, afforded the coordination polymers having the general stoechiometric formula of the type M(tr2ad)Cl2 (M = Zn,1; Cu, 2; Cd, 3; Ni, 4; Co, 5). Preliminary ab initio X-ray powder diffraction analyses revealed that 1 developes into a 1-D polymeric chain, while 2 features a 2-D polymeric structure. Thermal-gravimetric analyses (TGA) showed relevant thermal robustness of all these materials, peaking up to the onset of decomposition set at 350 °C

Amino-decorated bis(pyrazolate) metal-organic frameworks for carbon dioxide capture and green conversion into cyclic carbonates

The novel Metal-Organic Frameworks (MOFs) M(BPZNH 2 ) (M = Zn, Ni, Cu) were prepared from the reaction of the corresponding metal acetates M(OAc) 2 ·nH 2 O and the organic linker 3-amino-4,4′-bipyrazole (H 2 BPZNH 2 ) under solvothermal conditions. H 2 BPZNH 2 was obtained straightforwardly from the reduction of the related nitro-compound using hydrazine as a reducing agent. The Zn(ii) polymer is characterized by a 3D porous network featuring tetrahedral metallic nodes and bridging BPZNH 22- anions defining the vertices and edges of square channels. The isostructural Ni(ii) and Cu(ii) MOFs show square-planar metallic nodes and bridging BPZNH 22- spacers at the vertices and edges of the rhombic channels of a 3D porous framework. All the MOFs were characterized in the solid state [(VT)-PXRD, IR, TGA-DTG]. The textural property analysis revealed that they are micro-mesoporous materials with BET specific surface areas (SSAs) falling in the 100-400 m 2 g -1 range. Zn(BPZNH 2 ), showing the highest SSA (395 m 2 g -1 ) and a prevalently microporous texture (micropore area = 69% of the accessible SSA), has been exploited as a CO 2 capture material: at T = 298 K and pCO 2 = 1 bar, the total gas uptake equals 3.07 mmol g -1 (13.5 wt% CO 2 ). Its affinity for CO 2 (isosteric heat of adsorption Q st = 35.6 kJ mol -1 ; CO 2 /N 2 Henry selectivity = 17; CO 2 /N 2 IAST selectivity = 14) is higher than that of its nitro-functionalized analogue and comparable to that of other amino-decorated MOFs from the literature. Finally, Zn(BPZNH 2 ) was tested as a heterogeneous catalyst in the reaction of CO 2 with activated epoxides bearing a -CH 2 X pendant arm (X = Cl: epichlorohydrin; X = Br: epibromohydrin) to give the corresponding cyclic carbonates at T = 393 K and pCO 2 = 1 bar under green (solvent- and co-catalyst-free) conditions. A good conversion of 47% and a TOF of 3.9 mmol(carbonate) (mmol Zn ) -1 h -1 were recorded with epibromohydrin

Carbon Dioxide Capture and Utilization with Isomeric Forms of Bis(amino)-Tagged Zinc Bipyrazolate Metal\u2013Organic Frameworks

Aiming at extending the tagged zinc bipyrazolate metal\u2013organic frameworks (MOFs) family, the ligand 3,3\u2019-diamino-4,4\u2019-bipyrazole (3,3\u2019-H2L) has been synthesized in good yield. The reaction with zinc(II) acetate hydrate led to the related MOF Zn(3,3\u2019-L). The compound is isostructural with its mono(amino) analogue Zn(BPZNH2) and with Zn(3,5-L), its isomeric parent built with 3,5-diamino-4,4\u2019-bipyrazole. The textural analysis has unveiled its micro-/mesoporous nature, with a BET area of 463 m2 g 121. Its CO2 adsorption capacity (17.4 wt. % CO2 at pCO2 = 1 bar and T = 298 K) and isosteric heat of adsorption (Qst = 24.8 kJ mol 121) are comparable to that of Zn(3,5-L). Both Zn(3,3\u2019-L) and Zn(3,5-L) have been tested as heterogeneous catalysts in the reaction of CO2 with the epoxides epichlorohydrin and epibromohydrin to give the corresponding cyclic carbonates at T = 393 K and pCO2 = 5 bar under solvent- and co-catalyst-free conditions. In general, the conversions recorded are higher than those found for Zn(BPZNH2), proving that the insertion of an extra amino tag in the pores is beneficial for the epoxidation catalysis. The best catalytic match has been observed for the Zn(3,5-L)/epichlorohydrin couple, with 64 % conversion and a TOF of 5.3 mmol(carbonate) (mmolZn) 121 h 121. To gain better insights on the MOF-epoxide interaction, the crystal structure of the [epibromohydrin@Zn(3,3\u2019-L)] adduct has been solved, confirming the existence of Br c5 c5 c5(H) 12N non-bonding interactions. To our knowledge, this study represents the first structural determination of a [epibromohydrin@MOF] adduct